A process for isolating an antibody against insulin has, a unit operation, the reaction of the antibody with the antigen in a continuous stirred tnk reactor. The reaction product is a precipitate that is continuously removed from the reactor with 10% of the solution, which is mouse serum. Since insulin is an expensive reagent, only stoichiometric amounts can be added to the mouse serum, which contains 8 mg/liter of anti-insulin. If this particular monoclonal antibody precipitates with its antigen in a 1:1 ratio, how many milligrams of insulin must be added to the reactor per hour to process 100ml of mouse serum per hour.